On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee <edward.ming.lee@gmail.com> wrote:>I can't figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question: > >> For isolated application, the feedback divider has to be secondary side only >> and a TL431 used for error amp, into an opto, in the usual way. > >I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7 > >https://www.onsemi.com/pub/Collateral/TL431-D.PDF > >I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?For 12V, you'd need to recalculate your voltage divider, regardless of the regulation method intended. A 60W shunt regulator? Don't forget a collector resistor to soak up some of that power loss. Silicon resistors, loosely applied, are expensive and prone to failure. The only apps in your reference that used pnp power devices were for a crowbar circuit and for a switching converter; chaotic after an extra inversion. RL
24V to 500-1000V, 20W floating DC-DC converter
Started by ●July 21, 2020
Reply by ●September 9, 20202020-09-09
Reply by ●September 9, 20202020-09-09
On Wed, 09 Sep 2020 09:03:01 -0400, legg <legg@nospam.magma.ca> wrote:>On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee ><edward.ming.lee@gmail.com> wrote: > >>I can't figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question: >> >>> For isolated application, the feedback divider has to be secondary side only >>> and a TL431 used for error amp, into an opto, in the usual way. >> >>I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7 >> >>https://www.onsemi.com/pub/Collateral/TL431-D.PDF >> >>I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)? > >For 12V, you'd need to recalculate your voltage divider, regardless >of the regulation method intended. > >A 60W shunt regulator? Don't forget a collector resistor to >soak up some of that power loss. Silicon resistors, loosely >applied, are expensive and prone to failure. > >The only apps in your reference that used pnp power devices >were for a crowbar circuit and for a switching converter; chaotic >after an extra inversion. >Ach - figure 19. At 12V, you're TL431 will likely overheat for a normal bipolar pnp - supplying 250mA of base current. You'd get better thermals and reliability with a zener and nmosfet. RL
Reply by ●September 9, 20202020-09-09
On a sunny day (Wed, 9 Sep 2020 05:21:42 -0700 (PDT)) it happened Edward Lee <edward.ming.lee@gmail.com> wrote in <cea1e1a3-9f20-4cce-bdba-0995a0730ba5n@googlegroups.com>:>I can't figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, >i am high-jacking this for a quick question: > >> For isolated application, the feedback divider has to be secondary side only >> and a TL431 used for error amp, into an opto, in the usual way. > >I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7 > >https://www.onsemi.com/pub/Collateral/TL431-D.PDF > >I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?Other suggestions are good. But in these days of green looking politicians I think the question: 'Cannot you use a 12V switcher controlled supply for efficiency" is justified. After all California is already warming up to the extreme. So maybe it would help the world if you told us what you are trying to load' so much. Of course if it is US DOD top secret but then I won't help anyways. Not with this precedent.
Reply by ●September 9, 20202020-09-09
On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee <edward.ming.lee@gmail.com> wrote:>I can't figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question: > >> For isolated application, the feedback divider has to be secondary side only >> and a TL431 used for error amp, into an opto, in the usual way. > >I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7 > >https://www.onsemi.com/pub/Collateral/TL431-D.PDF > >I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)?You could fry the TL431 at 5 amps out, from too much PNP base current. A p-channel mosfet would help there, instead of the PNP. But the answer could be 5K either way. -- John Larkin Highland Technology, Inc trk The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
Reply by ●September 9, 20202020-09-09
onsdag den 9. september 2020 kl. 16.28.15 UTC+2 skrev John Larkin:> On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee > <edward.ming.lee@gmail.com> wrote: > > >I can't figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question: > > > >> For isolated application, the feedback divider has to be secondary side only > >> and a TL431 used for error amp, into an opto, in the usual way. > > > >I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7 > > > >https://www.onsemi.com/pub/Collateral/TL431-D.PDF > > > >I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)? > > You could fry the TL431 at 5 amps out, from too much PNP base current. > A p-channel mosfet would help there, instead of the PNP. >or compound pair, if power npn/nchannel is preferable
Reply by ●September 9, 20202020-09-09
On Wednesday, September 9, 2020 at 7:28:15 AM UTC-7, John Larkin wrote:> On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee > <edward....@gmail.com> wrote: > >I can't figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question: > > > >> For isolated application, the feedback divider has to be secondary side only > >> and a TL431 used for error amp, into an opto, in the usual way. > > > >I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7 > > > >https://www.onsemi.com/pub/Collateral/TL431-D.PDF > > > >I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)? > You could fry the TL431 at 5 amps out, from too much PNP base current.5A max for the AWG22 wires. Actual current may be couple of As for an instant.> A p-channel mosfet would help there, instead of the PNP.OK.> But the answer could be 5K either way.OK, thanks.
Reply by ●September 9, 20202020-09-09
On Wednesday, September 9, 2020 at 5:57:17 AM UTC-7, legg wrote:> On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee > <edward....@gmail.com> wrote: > > >I can't figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question: > > > >> For isolated application, the feedback divider has to be secondary side only > >> and a TL431 used for error amp, into an opto, in the usual way. > > > >I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7 > > > >https://www.onsemi.com/pub/Collateral/TL431-D.PDF > > > >I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)? > For 12V, you'd need to recalculate your voltage divider, regardless > of the regulation method intended.It's for overcharging protection of the batteries. Once triggered, divider ratio will get lower, until the load shift to another one in the serial chain.> A 60W shunt regulator? Don't forget a collector resistor to > soak up some of that power loss. Silicon resistors, loosely > applied, are expensive and prone to failure.Yes, good idea.
Reply by ●September 9, 20202020-09-09
On Wednesday, September 9, 2020 at 8:52:19 AM UTC-7, Edward Lee wrote:> On Wednesday, September 9, 2020 at 5:57:17 AM UTC-7, legg wrote: > > On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee > > <edward....@gmail.com> wrote: > > > > >I can't figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question: > > > > > >> For isolated application, the feedback divider has to be secondary side only > > >> and a TL431 used for error amp, into an opto, in the usual way. > > > > > >I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7 > > > > > >https://www.onsemi.com/pub/Collateral/TL431-D.PDF > > > > > >I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)? > > For 12V, you'd need to recalculate your voltage divider, regardless > > of the regulation method intended. > It's for overcharging protection of the batteries. Once triggered, divider ratio will get lower, until the load shift to another one in the serial chain. > > A 60W shunt regulator? Don't forget a collector resistor to > > soak up some of that power loss. Silicon resistors, loosely > > applied, are expensive and prone to failure. > Yes, good idea.Actually, i only need to drop it couple of volts, to stop charging. So, emitter resistor (5 ohms, 10W?) might work.
Reply by ●September 9, 20202020-09-09
On Wed, 9 Sep 2020 08:42:20 -0700 (PDT), Edward Lee <edward.ming.lee@gmail.com> wrote:>On Wednesday, September 9, 2020 at 7:28:15 AM UTC-7, John Larkin wrote: >> On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee >> <edward....@gmail.com> wrote: >> >I can't figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question: >> > >> >> For isolated application, the feedback divider has to be secondary side only >> >> and a TL431 used for error amp, into an opto, in the usual way. >> > >> >I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7 >> > >> >https://www.onsemi.com/pub/Collateral/TL431-D.PDF >> > >> >I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)? >> You could fry the TL431 at 5 amps out, from too much PNP base current. > >5A max for the AWG22 wires. Actual current may be couple of As for an instant. > >> A p-channel mosfet would help there, instead of the PNP. > >OK. > >> But the answer could be 5K either way. > >OK, thanks.Actually, with the PNP, it doesn't need a b-e resistor. Once, about 60 years ago, people used leaky germanium transistors, so using b-e resistors became folklore. -- John Larkin Highland Technology, Inc trk The cork popped merrily, and Lord Peter rose to his feet. "Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
Reply by ●September 9, 20202020-09-09
On Wednesday, September 9, 2020 at 10:14:34 AM UTC-7, John Larkin wrote:> On Wed, 9 Sep 2020 08:42:20 -0700 (PDT), Edward Lee > <edward....@gmail.com> wrote: > > >On Wednesday, September 9, 2020 at 7:28:15 AM UTC-7, John Larkin wrote: > >> On Wed, 9 Sep 2020 05:21:42 -0700 (PDT), Edward Lee > >> <edward....@gmail.com> wrote: > >> >I can't figure out how to post new message with the new google group. A search of TL431 came up with this thread recently. So, i am high-jacking this for a quick question: > >> > > >> >> For isolated application, the feedback divider has to be secondary side only > >> >> and a TL431 used for error amp, into an opto, in the usual way. > >> > > >> >I need a 12V 5A High Current Shunt Regulator, using fig. 19 of page 7 > >> > > >> >https://www.onsemi.com/pub/Collateral/TL431-D.PDF > >> > > >> >I am using 10K for R1, 1.1K for R2. What should i use for Rbe of the pass transistor (TO-220 PNP)? > >> You could fry the TL431 at 5 amps out, from too much PNP base current. > > > >5A max for the AWG22 wires. Actual current may be couple of As for an instant. > > > >> A p-channel mosfet would help there, instead of the PNP. > > > >OK. > > > >> But the answer could be 5K either way. > > > >OK, thanks. > Actually, with the PNP, it doesn't need a b-e resistor. Once, about 60 > years ago, people used leaky germanium transistors, so using b-e > resistors became folklore.OK, i'll try a 5 ohm emitter resistor to limit the current. Once triggered, it will probably start to discharge into other cells, but that's fine.
